Conventionally, there is a well-known electric power system comprising: a power generation system having a generator driven by an engine; and a power source selector which is switched to alternatively select either an external power source or the generator as a power source supplied to each of power load groups.
The power source selector has power source switching units provided corresponding to the respective power load groups. Each of the switching units has means for detecting data concerning a value of electric power at its output side so as to detect data concerning a value of electric power to the power load group connected to the switching unit. A control mechanism in the power source selector calculates powers of all the power load groups by detecting data concerning the values of power to the respective power load groups, thereby controlling switching of the respective power source switching units.
Calculation of the used generated power share of all the power to loads in association with the above-mentioned control of the power source selector is effective for voltage control of the power generated by the generator so as to fully utilize the power of the generator. However, addition of such means as to detect power values to the respective power load groups for checking whether the generator or the external power source supplies power to each of the power load groups increases the whole electric power system in size and cost.
Further, each of the power source switching units provided corresponding to the respective power load groups requires networking with a controller for controlling generated power, switching for selection of power source, and setting of various parameters. In addition, the above-mentioned networking must ensure such mutual communication among the power source switching units as to make each of the power source switching units select the best power source. However, the wiring is complicated for the networking and communication among the plurality of power source switching units.